1. Field of The Invention
This invention relates to a printing material used for fabricate a printing plate and more particularly, to a printing material which is enabled to make a printing plate by laser engraving.
2. Description of The Prior Art
As is known in the art, printing plates such as for gravure printing are formed of a very large-sized, heavy metal roll. For the fabrication of the printing plate, a specific type of equipment is necessary with a number of complicated plate-making steps. In addition, a skilled technique for the fabrication of the plate is essential.
As a printing material, there have been used resin sheets such as a polyethylene sheet, which are flexible and light in weight. Moreover, the printing material is formed with fine pits by laser processing and, thus, engraving is now automated.
For the engraving of the printing material, the material is initially wound about a plate cylinder of a printing machine. Then, a laser beam emitted from a laser device such as a semiconductor laser is converted into a predetermined spot size by means of a focusing optical system and irradiated on the wound material. Where a plurality of pits are formed on the surface of the material, the plate cylinder is turned while moving the focusing optical system along the length of the cylinder. As a result, the laser beam is irradiated on the surface of the plate material at portions where pits are to be formed, thereby establishing a required number of pits therein. In this manner, a printing plate is obtained.
However, when a semiconductor laser is used to establish pits in the printing material in a manner as stated above, it takes a long time before the pits have been formed only by application of the laser beam. This is because of the low combustibility of the printing material.